1. Field of the Invention
The present invention relates to a compact light emitting module for optical communication incorporating a low-power driver and used as an optical transmitter for an ultra-high-speed optical emission system, and a light emitting unit used for the module.
2. Related Background Art
In light emitting modules for optical communication, laser diodes (LDs) are widely used as light emitting devices. In such a module, characteristics such as I-L characteristics indicating the relationship between the injection power to the LD and the output light power greatly depend on the temperature of the LD. To perform stable emission regardless of external temperature conditions, the temperature of the LD must be controlled to be constant. For an application demanding a wavelength stability of 1 mm or less, in particular, temperature control with a precision of 1.degree. C. or less is required.
LDs generate heat during operation. Various light emitting modules having cooling elements for cooling the LDs to remove the heat generated by the LDs are known. For example, the light emitting module disclosed in Japanese Patent Laid-Open No. 8-195528 is available.
FIGS. 8A and 8B show the light emitting module disclosed in this reference. FIG. 8A is an upper view of the module without the package. FIG. 8B is a sectional view of the module. Referring to FIGS. 8A and 8B, an LD 104 is mounted on a Peltier cooler 112 serving as a cooling element through a Kovar base 128 and a copper laser carrier 130. Since temperature control is performed by using the Peltier cooler 112, a thermister 134 for measuring the temperature near the LD 104 is placed near the LD 104. With this arrangement, fine temperature control can be performed for the LD 104 to stabilize the emission characteristics.